The present invention relates to a radiation measuring device capable of detecting radiation such as a particle beam, a particle beam therapy device provided with the radiation measuring device, and a method for calculating a dose profile of a particle beam.
For particle beam therapy, a scanning irradiation method tends to be widely used.
In the scanning irradiation method, a target is divided into microscopic regions (hereinafter referred to as spots) that are each irradiated with a beam with a small radius (of 1σ=3 to 20 mm). After a predetermined dose has been applied to a certain spot, the beam irradiation is stopped and then, the next spot is scanned with the beam. Scanning electromagnets are used for scanning the beam in a direction perpendicular to its propagation direction (Hereinafter, the propagation direction is referred to as “a depth direction”; the direction perpendicular to the depth direction is referred to as “a lateral direction”). After a predetermined dose has been applied to each of all spots existing at a certain depth, the beam is next scanned in the depth direction. The beam scanning in the depth direction requires an energy change of the beam, the energy change being made by an accelerator or a range shifter. Thus, uniform doses are applied to all the spots or the overall target.
In this case, an operator uses a radiation measuring device to measure a position irradiated with the beam and a depth dose profile and analyzes results of the measurement so as to determine whether or not a particle beam therapy device is appropriately adjusted.
As a conventional radiation measuring device, a multilayer ionization chamber (MLIC) that has a structure of parallel plate ionization chambers stacked in a depth direction and is capable of measuring a depth dose profile of a particle beam at the same time is known (refer to JP-2011-153833-A and ‘M. Shimbo, et al., “Development of a Multi-layer Ion Chamber for Measurement of Depth Dose Distributions of Heavy-ion Therapeutic Beam for Individual Patients”, NIPPON ACTA RADIOLOGICA 2000 60 274-279’).